JP2000101835A - Image forming device, image forming system and computer readable recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce occurrence of moire without deteriorating gradation and resolution. SOLUTION: An image processing section 14 detects a screen angle of an image of an original. Then a dot dither to be used for print is selected among a plurality of dot dithers with different screen angles that are prepared so that the screen angle of the image of the original is not identical to that of the dither pattern of the print image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for expressing an input image in gray scale by screen processing, and more particularly to an image forming apparatus capable of performing gray scale expression while suppressing occurrence of moire.

[0002]

2. Description of the Related Art Conventionally, when an input image having a gradation is output by an output device having a smaller number of gradations, a plurality of gradations are required in order to secure a higher number of gradations per pixel. The screen processing using the dither of the pattern is performed.

When a pseudo halftone is reproduced by using a dither having a specific screen angle such as a halftone dot dither among the dithers used in this screen processing, when a specific halftone original is output, the original is reproduced. There is a problem that moire based on the screen angle between the halftone dot and the dither pattern occurs.

When the difference between the number of halftone dots of a document and the number of dither lines of an output device is small and the screen angle of the document and the dither screen angle are almost the same, moire having a particularly low frequency tends to occur.

By the way, the number of halftone dots and the screen angle of a general document are not particularly determined, and there are various screen angles for each color (C, M, Y). Therefore, when a pseudo halftone is reproduced using a specific dither pattern, moire occurs in any halftone dot document.

In order to suppress the occurrence of moire, the dither pattern is made finer, that is, the number of lines is increased, and the number of lines of a halftone dot document where moire occurs is increased to a level where there is substantially no problem. However, when the number of lines is increased in this way, the output device must have a high resolution in order to secure the gradation, and the area modulation and intensity modulation of one dot or less must be performed. You must be able to control it. Therefore, the output device is required to have a very high performance, and the output device is less feasible in terms of cost.

As a technique for suppressing the occurrence of such moiré without requiring a high-performance output device,
It is presumed that moire has occurred when low-frequency peaks that do not exist in the frequency plane of the image before the screen processing appear on the frequency plane of the image before the screen processing on the frequency plane of the image after the screen processing, respectively. There is a technique for selecting an optimum screen size (Japanese Patent Laid-Open No. 8-2).
No. 3444). According to such a technique, the output device does not require such high performance, so that application of this technique to the market is relatively easy.

[0008]

However, in such a conventional technique, occurrence of moiré is estimated from an image after screen processing, and when occurrence of moiré is estimated, the screen size is changed. Therefore, when the screen size is made larger than the original size, the resolution is reduced. On the contrary, when the screen size is made smaller than the original size, there is a disadvantage that the gradation is deteriorated. .

Generally, the screen size of an output device is
In consideration of the performance of the output device, the size is set so that the balance between the resolution and the gradation is the best. Therefore, if the screen size is changed to suppress the occurrence of moiré, either the resolution or the gradation is adversely affected, which naturally affects the quality of the output image.

In order to solve the above problems, the present invention detects a screen angle of a document image and prepares the screen angle of the document image so that the screen angle of the dither pattern of the print image does not become the same. It is an object of the present invention to provide an image forming apparatus in which a halftone dot dither used for an output device can be selected from a plurality of dither patterns having different screen angles, and a gradation expression can be performed while suppressing the occurrence of moire.

[0011]

The present invention for achieving the above object is constituted as follows for each claim.

According to a first aspect of the present invention, there is provided a reading means for reading a document, a screen angle detecting means for detecting a screen angle of the document read by the reading means, and a screen of the document detected by the screen angle detecting means. Dither pattern setting means for switching and setting a plurality of dither patterns having different screen angles according to the angle;
A printing unit for reproducing a pseudo halftone using the dither pattern set by the dither pattern setting unit.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the dither pattern setting means includes a dither pattern having a screen angle different from the screen angle of the document detected by the screen angle detection means. It is characterized in that a pattern is set.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the screen angle detecting means detects a screen angle of a document read by the reading means for each of C, M, and Y colors. Then, the dither pattern setting means sets C, M, Y, and C in accordance with the screen angle of each color detected by the screen angle detecting means.
A plurality of dither patterns having different screen angles are switched and set for each color of K.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the screen angle detecting means includes an R, G, B of the original read by the reading means.
Color conversion means for converting the image data of C, M, Y, and K into image data of C, M, Y, and K;
The image processing apparatus further comprises: resolution conversion means for converting the M, Y, and K image data into high-resolution image data; and image data storage means for storing the high-resolution image data converted by the resolution conversion means. A screen angle for each of C, M, and Y colors is detected based on image data stored in the data storage means.

According to a fifth aspect of the present invention, there is provided a reading means for reading a document, a screen angle detecting means for detecting a screen angle of the document read by the reading means, and a screen of the document detected by the screen angle detecting means. Dither pattern setting means for switching and setting a plurality of dither patterns having different screen angles according to the angle;
An image reading apparatus comprising: print data generating means for generating print data for reproducing pseudo halftones using the dither pattern set by the dither pattern setting means.

According to a sixth aspect of the present invention, there is provided a screen angle detecting means for detecting a screen angle of a document from input image data of the document, and a screen angle of the document detected by the screen angle detecting means. Dither pattern setting means for switching and setting a plurality of dither patterns having different screen angles; and print data generating means for generating print data for reproducing pseudo halftones using the dither pattern set by the dither pattern setting means. A printer controller comprising:

According to a seventh aspect of the present invention, there is provided a reading device for reading a document, a screen angle of the document read by the reading device being detected, and a plurality of screen angles having different screen angles according to the detected screen angle of the document. An image forming system comprising: a printer controller that switches and sets the dither pattern of the image forming apparatus; and a printer that reproduces a pseudo halftone using the dither pattern set by the printer controller.

According to an eighth aspect of the present invention, there is provided a procedure for reading a document, a procedure for detecting a screen angle of the read document, and a plurality of dither patterns having different screen angles according to the detected screen angle of the document. This is a computer-readable recording medium in which a program for causing a computer to execute a procedure for switching and setting and a procedure for reproducing a pseudo halftone using the set dither pattern is recorded.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, a plurality of halftone dithers (dither patterns) having different screen angles are prepared for each color as dither patterns for output, and the screen angle of the original image is detected. Set a screen dither with a screen angle different from the screen angle of the original image according to the
It is possible to suppress the occurrence of moire in a printed image.

Embodiments of the present invention that can realize this will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus according to the present invention.

This image forming apparatus comprises a scanner unit 10, a printer unit 20, and a personal computer 30. The scanner unit 10 has a scanner 12 and an image processing unit 14. The scanner 12 includes CCDs for G (green), R (red), and B (blue).
Scans a document image and outputs 8-bit image data of each color of RGB. The image processing unit 14 has a function of converting image data output from the scanner 12 from RGB to C (cyan), M (magenta), Y (yellow), and K (black).

The printer unit 20 includes a printer engine 22
And a controller 24. The printer engine 22 inputs color image data of four colors of CMYK output from the image processing unit 14 and performs color printing. The controller 24 inputs information about printing from a personal computer, which will be described later, and outputs a calculation result to the printer engine 2.
2 while outputting the calculation result to a personal computer.

A personal computer (PC) 30 is a commonly used computer, and is connected to the scanner 12 via a SCSI interface and to the controller 24 via a printer interface.
When a scan signal is output from the personal computer 30, the scanner 12 starts scanning and reads a document image, and the printer engine 22 receives information based on the print-related information input from the personal computer 30 via the controller 24. Make a color print. Note that the scanner unit 10 and the printer unit 20 are each independently a personal computer 3
It is configured so that an image can be output to the PC 0 and an image can be input from the personal computer 30.

FIG. 2 is a block diagram showing a detailed configuration of the image processing section 14 shown in FIG. The memory 50 of the image processing unit 14 stores the RGB colors 8 output from the scanner 12.
Bit image data is stored for each color.

The LOG converter 51 converts image data read from the memory 50 from reflectance data to density data for each color. The color conversion unit 52 converts the image data converted into the density data by the LOG conversion unit 51 into RGB data.
Is converted into image data of three colors CMY.

The UCR / BP processing unit 53 includes a color conversion unit 52
The CMY three-color image data converted by
The image data is converted into MYK four-color image data. The image correction unit 54 converts the CM converted by the UCR / BP processing unit 53
For each color of YK, MTF correction, smoothing filtering processing, and γ correction to match the output characteristics of the printer engine 22 are performed. The gamma correction is performed differently depending on the screen angle of the halftone dither (dither pattern). The image correction unit 54 performs different filtering processing according to the result of determination as to whether it is a character portion or a photographic portion determined by an image region determination unit 57 described later.

The resolution conversion section 55 converts the image data output from the image correction section 54 into data having a higher resolution. In the present embodiment, the resolution converter 5
5 indicates a reading resolution of 300 dpi of the scanner 12,
The main scanning direction 1200d which is the minimum unit of the dither table
The resolution is increased by converting the image to a resolution of 600 × pi in the sub-scanning direction.

The dither processing unit 56 converts the image data (multi-value data) whose resolution has been increased by the resolution conversion unit 55 into binary data, and the screen angle of the image data is the halftone dot dither (dither pattern). The halftone dither to be used is set in the dither table in comparison with the screen angle. Note that the dither tables (first and second dither tables) correspond to the R
The dither table is stored in the OM, and the halftone dither having a specific screen angle is stored in the dither table so that pseudo halftone can be reproduced without generating moiré.

The printer engine 22 includes a dither processing unit 5
A color image is printed based on the image data output from the printer 6. The image area discriminating section 57 discriminates, for each area, whether it is a character section or a photographic section from the 8-bit RGB color image data extracted from the memory 50 and outputs the discrimination result to the image correcting section 54. is there. CPU 58
Controls the operation of all blocks constituting the image processing unit 14 in a comprehensive manner.
Is operated for each color, and when it is operated repeatedly four times, 1
One color print will be obtained.

Next, a process for detecting the screen angle of the document and setting a dither pattern free from moiré will be described in detail with reference to a flowchart.
FIG. 3 is a flowchart illustrating a processing procedure for detecting a screen angle of a document image and setting a halftone dither,
FIG. 4 is a flowchart for detecting the screen angle of the document image.

First, the scanner 12 scans an original image, converts the scanned image into 8-bit data for each color of RGB, and outputs the data.
The memory 50 stores the output image data for each color (S1).

The image area determination section 57 reads out image data for one color (for example, R) stored in the memory 50 and detects the screen angle of the original image (S
2). This screen angle is detected as follows according to the procedure of the flowchart shown in FIG.

First, the image area determining section 57 divides the read image data into several blocks for each area (S21). Then, the average value I of the brightness for each divided area
ave is calculated (S22). When the calculation of the average value of the brightness is completed for all the areas, the average value of the brightness Iave
Extracts an area between the lower limit L1 of brightness and the upper limit L2 of brightness set in advance. The reason for searching for an area where the brightness falls within a certain range is that it is necessary to remove a background portion having a high brightness or an area having a low brightness that is unsuitable for recognizing a halftone screen pattern (S23).

Next, the image data is binarized using the average value of the brightness of each extracted area as a threshold. FIG. 5 schematically shows the image data after the binarization.
(A) or (B). The binarized halftone image illustrated in FIG. 5A has a screen angle of 45 ° and the number of lines of 133 lines / inch, and the binarized halftone image illustrated in FIG. The halftone image has a screen angle of 75 ° and the number of lines is 133 lines / inch. These two angles correspond to the two screen angles of the halftone dither prepared in the dither processing unit 56 (S24).

Further, a specific pattern (a pattern matching with the dither pattern shown in FIG. 6) in each area is detected and the number thereof is counted. This process is performed in the following procedure.

When the binarized image data becomes a halftone image as shown in FIG. 5A, the screen angle of this halftone image is determined by the halftone dot prepared in the dither processing unit 56. In order to determine whether or not the angle is the same as the dither screen angle, matching between this halftone dot image and the 4 × 3 detection pattern shown in FIG. 6 is determined. When the number of lines of the halftone image and the number of lines of the halftone dot dither are largely different from each other, a large moire does not occur. Therefore, a detection pattern having a number of lines close to the dither pattern of the halftone dot dither is prepared.

The judgment of this matching is made, for example, by referring to FIG.
When the inverted L-shaped 4 × 3 detection pattern (for detecting a screen angle of 45 °) on the left side of (A) is used, first, this detection pattern is superimposed on the upper left of the halftone image of FIG. It is determined whether the 4 × 3 pixel of the detection pattern matches the 4 × 3 pixel of the detection pattern (the white and black patterns match), and if they match, the count is incremented by 1; do not do. Next, the detection pattern is shifted to the right (in the X direction) by one pixel, and it is determined whether or not 4 × 3 pixels of the halftone image and 4 × 3 pixels of the detection pattern match. The count is incremented by 1 and not counted if they do not match. In this manner, the detection pattern is moved in the X direction one pixel at a time to the right end pixel of the halftone dot image to determine the matching. When the right end is completed, the detection pattern is further lowered by one line (Y direction). In the same manner, the line is moved one pixel at a time from the left end to the right end to determine the matching. When the matching determination is completed up to the bottom line of the halftone dot image, the number of times of matching is grasped from the count number. .

Next, for example, an X-shaped 4 × 3 detection pattern on the left side of FIG. 6B (for detecting a screen angle of 75 °)
Is used to determine the matching in the same manner as described above, and how many times the matching has been performed is grasped from the count number. If detection patterns of different screen angles are prepared,
Using this detection pattern, matching is determined, and the number of times of matching is grasped (S25).

As described above, when the number of times of matching is detected for each detection pattern using the detection patterns having different screen angles, it is determined which screen angle of the detection pattern having the largest number of matching times was. , The angle is defined as the screen angle of the document image. For example, in the above case, if the number of times of matching of the detection pattern with a screen angle of 25 ° is 100 and the number of times of matching of the detection pattern with a screen angle of 75 ° is 35,
The screen angle of this halftone image is determined to be 25 °.

When the halftone image has a screen angle other than the screen angles of the two detection patterns, no large moire occurs even if the halftone dither is set to any screen angle. The halftone dither of the screen angle with the smaller number of times is automatically set (S26).

When the screen angle of the original image for C (cyan) is detected by the above processing (S3), the screen diagonal dot dither of this color (cyan) to be used at the time of printing is used. 1 dither table), the screen angle is
Since the occurrence of moire is a concern, a halftone dot dither (second memory) having a screen angle different from this screen angle is stored in a ROM (a memory (not shown) existing in the dither processing unit 56) in which the dither table is written. Dither table). On the other hand, if the two screen angles do not match, there is no danger of moiré occurring even if the halftone dither is used. Therefore, the set halftone dither (first dither table) is stored in the ROM. Set (S
4).

When the screen angles match, the image correction unit 54 sets a γ table corresponding to the changed halftone dither. The reason for resetting the γ table in this way is to change the halftone dot dither, since the density reproduction characteristic will be slightly changed, and to cope with this change (S5).

The printer engine 22 prints C (cyan) image data by applying the set halftone dither to the image data corrected by the set γ table.

The image correction unit 54 performs the above processing in order for the colors M (magenta) and Y (yellow), and sets the dot dither and the γ table for each color, and sequentially sets each color. The color print is completed by printing each time.

The reason why the processing is performed for each color is that the screen angle of the halftone image is different for each color of CMY. For this reason, the screen angle of the C (cyan) halftone image is checked by the R data, the screen angle of the M (magenta) halftone image is checked by the G data, and the screen angle of the Y (yellow) original image is checked by the B data. Are checked (S6).

In the above embodiment, the mode in which only the angle at which moiré is likely to occur, that is, only the screen angle (45 ° or 75 °) of the halftone dither which the system has, has been described. The number of types may be increased and other screen angles may be detected. In this case, a type of halftone dither corresponding to the type of the detection pattern is prepared, and the type of halftone dither to be set is changed according to the detected screen angle.

The screen angle is detected by moving the detection pattern pixel by pixel and line by line. However, if the printing speed is more important than the detection accuracy, the movement in the X direction should be three times. The detection speed may be increased by moving the detection pattern stepwise (moving in blocks), such as moving in the Y direction every four lines for each pixel.

Next, a second embodiment different from the above-described embodiment will be described. FIG. 7 is a block diagram illustrating a schematic configuration of the image forming apparatus according to the present embodiment. The function of each block shown in FIG.
Although the description is omitted because it is almost the same as that of the first embodiment, the only difference is that the resolution of the resolution conversion unit 55 is from the reading resolution 300 dpi of the scanner 12 to the main scanning direction 600 dpi × the sub operation direction 600 dpi which is the minimum unit of the dither table. To be converted to
That is, the result of the resolution conversion unit 55 is stored in the memory 50. The image processing unit 14 stores, in the memory 50, 8-bit image data of each color of RGB regarding the document image sent from the scanner 12 (S11).

Next, the image processing unit 14
The LOG conversion unit 51 converts the density data from RGB image data to CMY image data, and converts the density data from RGB image data to CMY image data. BP processing unit 5
3 further converts the CMY image data into CMYK image data.
Correction, filtering processing of smoothing, and γ correction in accordance with the output characteristics of the printer engine 22 are performed. Finally, the image data is converted into high-resolution image data by the resolution conversion unit 55 and stored in the memory 50 again. The memory 50 stores image data of four colors of CMYK with high resolution, and the stored image is an image of a partial area of the image read by the scanner 12 (S12).

Next, the image area determining section 57
The CMYK four-color image data of high resolution stored in 0 is read out one color at a time, and the screen angle of the document image is obtained. That is, the screen angle of the cyan halftone dot image is calculated based on the image data of C (cyan), and M (magenta)
Then, the screen angles of the magenta halftone dot images are determined based on the image data of (1), and then the screen angles of the Y (yellow) and B (black) halftone images are determined (S13).

This screen angle is detected as follows in accordance with the procedure of the flowchart shown in FIG. First, the image area determination unit 57 divides the image data stored in the memory 50 into several blocks for each area (S31). Then, an average value Dave of the density is calculated for each of the divided areas (S32). When the calculation of the average value of the density is completed for all the areas, the average value Dav of the density is calculated.
e is a preset lower limit of density D1 and an upper limit of density D2
And extract the area in between. The reason for searching for an area in which the density is within a certain range is that it is necessary to remove an area where the density is too low or an area where the density is too high to recognize the halftone screen pattern (S3).
3).

A smaller area is set in each of the extracted areas (S34), a pixel exhibiting the highest density in the set area is determined, and the pixel is set as a target pixel (S35). Next, the average value of the density of the surrounding pixels located in the directions of 0 °, 15 °, 30 °, 45 °, 60 °, and 75 ° vertically from the target pixel is calculated (S36). Then, the angle at which the average value of the density is the highest is obtained, and the count of the angle is incremented by +1 (S37).
The same processing is performed for each small area for each area, and the number of detections is counted for the angle having the highest density average value for each angle. As a result, the angle with the largest count is set as the screen angle of the halftone dot image of that color (S38).

The above processing is sequentially performed for each color of CMYK, and it is determined whether or not the screen angle of the halftone image of each color matches the screen angle of the halftone dither to be used for printing. For example, C
When the screen angle of the halftone image (original) for (cyan) is detected (S14), the screen angle of the halftone image of this color is equal to the screen angle of the halftone dither of this color to be used for printing. If they match, the ROM in which the dither table is written (the dither processing unit 56
The dither processing section 56 sets a halftone dot dither (second dither table) having a different screen angle to the dither processing section 56.
On the other hand, if they do not match, the set halftone dither (first dither table) is set as it is.

The above processing is performed for the colors M (magenta), Y (yellow), and K (black), and the color printing is completed. The reason why the process is performed for each color is that the screen angle of the halftone dot image is different for each color of CMYK. For this reason, C (cyan) is determined by R data.
Check the screen angle of the halftone dot image of
The screen angle of the (magenta) halftone image is checked, the screen angle of the Y (yellow) document image is checked by the B data, and the screen angle of the K (black) document image is checked by the K data (S15). .

If the screen angles match, the gamma table corresponding to the changed halftone dither is set in the image correction unit 54. The reason for resetting the γ table in this way is that when the dot dither is changed, the density reproduction characteristic also slightly changes, so that this change is dealt with (S16). As described above, when the setting of the halftone dither is completed and the setting of the γ table is completed, a print start instruction is issued to the printer engine 22, and the printer engine 22 outputs the γ set for each color.
Color printing is performed by applying the halftone dither (written in the dither table) set for each color to the image data corrected in the table (S17).

In the above embodiment, the angles at which moiré is likely to occur are 0 °, 15 °, 30 °, and 30 °.
Although the mode in which only 45 °, 60 °, and 75 ° are detected has been described, a screen angle other than these may be detected.

In the above embodiment, the case where the technical idea according to the present invention is applied to the image forming apparatus has been described. However, the scanner 12 and the image processing section 14 shown in FIG. It is also possible to apply to the formed image reading device or a printer controller formed by housing the image processing unit 14 and the controller 24 shown in FIG. 1 in one housing.

Further, the scanner unit 10, the printer unit 20, and the computer 30 for controlling the scanner unit 10 and the printer unit 20 of FIG. 1 are components as a reading device, a printer, and a printer controller, respectively, and these are connected to each other. The present invention is also applicable to a configuration in which an image forming system is configured.

Further, the procedure shown in FIG. 3 and FIG.
And the procedure shown in FIG. 9, i.e., reading a document, detecting the screen angle of the document, switching and setting a dither pattern according to the screen angle, and printing a pseudo halftone with the dither pattern. And a computer forming a part of an image forming apparatus, an image reading apparatus, a printer controller, and an image forming system based on the recording medium. It is also possible to realize the technical idea of the present invention.

[0061]

As is apparent from the above description, according to the present invention, the following effects can be obtained for each claim.

According to the image forming apparatus of the first to fourth aspects, printing is performed using a dither pattern having a screen angle different from that of the original, so that the printing performance of the apparatus is not particularly improved. Further, occurrence of moiré can be reduced without deteriorating the gradation and resolution.

According to the image reading apparatus of the fifth aspect,
Since the print data is created using a dither pattern having a screen angle different from that of the original, it is possible to reduce the occurrence of moire when printing.

According to the printer controller of the sixth aspect, since printing can be performed using a dither pattern having a screen angle different from that of the original, occurrence of moire can be reduced.

According to the image forming system of the present invention, printing is performed using a dither pattern having a screen angle different from that of the original, so that the printing performance of the system is not particularly improved, and the gradation is improved. The occurrence of moiré can be reduced without deteriorating the quality or resolution.

According to the computer-readable recording medium of the present invention, by causing the computer to read the recording medium, the computer functions as a part of the image forming apparatus, the image reading apparatus, the printer controller, and the image forming system. Will be able to do it.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus according to the present invention.

FIG. 2 is a block diagram illustrating a detailed configuration of an image processing unit illustrated in FIG. 1;

FIG. 3 is a flowchart showing a processing procedure for detecting a screen angle of a document image and setting a dither pattern.

FIG. 4 is a flowchart for detecting a screen angle of a document image.

FIG. 5 shows an example of a halftone image after binarization. The halftone image after binarization shown in (A) has a screen angle of 45 ° and the binarization image shown in (B). The subsequent halftone image has a screen angle of 75 °.

FIG. 6 is an example of a detection pattern used for detecting a screen angle of a halftone dot image. A detection pattern shown in FIG. 6A is for detection at a screen angle of 45 °, and a detection pattern shown in FIG. The screen angle is for detection of 75 °.

FIG. 7 is a block diagram illustrating a schematic configuration of an image forming apparatus according to a second embodiment.

FIG. 8 is a flowchart illustrating a processing procedure for detecting a screen angle of a document image and setting a dither pattern according to the second embodiment.

FIG. 9 is a flowchart for detecting a screen angle of a document image according to the second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... scanner part (reading means), 12 ... scanner (reading means), 14 ... image processing part (printer controller), 20 ... printer part (printer), 22 ... printer engine (printing means), 24 ... controller, 30 ... Personal computer (PC), 50: memory (image data storage unit), 52: color conversion unit (color conversion unit), 53: UCR / BP processing unit (color conversion unit), 55: resolution conversion unit (resolution conversion unit), 56: dither processing unit (dither pattern setting means, screen angle detecting means, print data generating means) 57: image area determining unit (screen angle detecting means) 58: CPU (printing means)

Continued on the front page F-term (reference) 2C262 AA24 AA26 AA27 AB01 AC04 BA02 BB25 BB27 EA04 5C072 AA01 AA03 BA18 BA19 EA05 QA14 UA07 UA11 UA13 UA17 UA18 UA20 XA04 5C077 LL03 MM03 MP08 NN09 PP02 PP19 HB02 HB03 HB12 JA23 LA31 LA37 LC04 LC14 MA02 MA11 NA02 PA03

Claims (8)

[Claims] 1. A reading means for reading a document, a screen angle detecting means for detecting a screen angle of the document read by the reading means, and a screen angle according to a screen angle of the document detected by the screen angle detecting means. An image forming apparatus comprising: dither pattern setting means for switching and setting a plurality of different dither patterns; and printing means for reproducing a pseudo halftone using the dither pattern set by the dither pattern setting means. . 2. The image forming apparatus according to claim 1, wherein the dither pattern setting unit sets a dither pattern having a screen angle different from a screen angle of the document detected by the screen angle detection unit. . 3. The screen angle detecting means detects a screen angle of a document read by the reading means as C, M, or
Y, and the dither pattern setting means detects a plurality of dithers having different screen angles for each of C, M, Y, and K in accordance with the screen angle of each color detected by the screen angle detecting means. The image forming apparatus according to claim 1, wherein the pattern is set by switching. 4. A color conversion means for converting R, G, B image data of a document read by said reading means into C, M, Y, K image data, said color conversion means comprising: Resolution conversion means for converting the C, M, Y, and K image data converted by the means into high-resolution image data; and image data storage means for storing the high-resolution image data converted by the resolution conversion means. The image forming apparatus according to claim 3, further comprising: detecting a screen angle for each of C, M, and Y colors based on the image data stored in the image data storage unit. 5. A reading means for reading a document, a screen angle detecting means for detecting a screen angle of the document read by the reading means, and a screen angle according to the screen angle of the document detected by the screen angle detecting means. Dither pattern setting means for switching and setting a plurality of different dither patterns, and print data generating means for generating print data for reproducing pseudo halftones using the dither pattern set by the dither pattern setting means. An image reading apparatus characterized by the above-mentioned. 6. A screen angle detecting means for detecting a screen angle of a document from input image data of the document, and a plurality of dithers having different screen angles according to the screen angle of the document detected by the screen angle detecting means. A printer comprising: dither pattern setting means for switching and setting a pattern; and print data generating means for generating print data for reproducing pseudo halftones using the dither pattern set by the dither pattern setting means. controller. 7. A reading device for reading a document, detecting a screen angle of the document read by the reading device, and switching and setting a plurality of dither patterns having different screen angles according to the detected screen angle of the document. An image forming system, comprising: a printer controller that performs a pseudo-halftone using a dither pattern set by the printer controller. 8. A procedure for reading a document, a procedure for detecting a screen angle of the read document, a procedure for switching and setting a plurality of dither patterns having different screen angles according to the detected screen angle of the document, And a computer-readable recording medium storing a program for causing a computer to execute a pseudo halftone using a set dither pattern.